[48.09] Will Cassini Detect Meteors in Saturn's Rings?

To evaluate Cassini's prospects for detecting meteoroid
impacts on Saturn's rings, we assume an isotropic cometary
flux striking the rings after being focused by Saturn's
gravity for individual incoming directions (Cuzzi and
Durisen 1990). The most energetic impacts occur in Saturn's
shadow where Saturn's and the rings orbital velocities
align. To estimate how the light flash's intensity depends
on a meteoroid's velocity we combine laboratory results
(Burchell et al. 1996) with modelling (Artemieva
et al. 2000) developed for Leonid meteoroids hitting the
Moon. For Cassini at ~13 Saturn radii looking near
synchronous orbit, impacts of 10-kg meteoroids should be
visible as 6th to 9th magnitude flashes lasting < 0.03 s;
they should appear every ~2\times 104 s in the WAC
field of view (cf. Showalter 1998). Less luminous flashes
coming from smaller bodies appear a few times more
frequently. The NAC sees fewer 10-kg events (~4\times
105 s) but more small impacts.

Meteoroid impacts may be associated with Saturn's spokes
(Goertz and Morfill 1983). The formation rate of spokes is
consistent with the impact rate for 10-kg meteoroids
(10-4 per second per radian; Cuzzi and Estrada 1998).
This meteoroid size is also sufficient to produce the
neutral gas that, after photoionization, drifts to account
for the spoke event (Morfill and Goertz 1983). Very large
boulders are prominent in the central B ring since the
nominal size distribution for ring particles starts at about
10 kg. Thus most of a typical meteoroid's collisional
kinetic energy will be dissipated.

Since it may be problematic to distinguish such infrequent
signals from cosmic ray hits on the CCD, we will asses
strategies to recognize such events. For example, after the
emergence of the target area from the shadow, Cassini will
trace back spoke locations to search for the flashes of the
initiating impact. Alternatively we will look for streaks
(``Shooting stars'') crossing diaphanous rings.